1. Field of the Invention
This invention in the preferred embodiment relates to a lighting device which emits a light that is used for illumination and color discrimination when it is projected on an external surface. It performs these tasks throughout a range of power and with a minimum of infrared emissions. More specifically, the invention relates to a lighting device which synthesizes its projected radiant energy from two or more light sources of differing spectral distributions. It uses the characteristics of the different light sources to interact photometrically and/or electrically to create an emitted beam of light which provides color discrimination over an extended range of powers. Other features of the invention include improved efficiency and power condition monitoring. The invention has application in devices energized by either power lines or batteries.
2. Related Art
Lighting devices which are used to illuminate are also frequently required to provide color discrimination when they are projected upon multicolored surfaces. White light is the most commonly used because white provides color discrimination for all of the colors of the spectrum. However, spectral distributions other than white may also find application in situations where limited color discrimination is acceptable. Lighting devices of this nature are frequently dimmed and when that feature is provided, it is desirable that the device maintain its ability to accurately discriminate between the required colors throughout the full required range of dimming of the emitted illumination. It is also desirable that a single control effect the dimming while minimizing changes in the discrimination of colors.
The invention provides a lighting device that combines lamp sources for color discrimination and also retains the color discrimination as the device is dimmed.
Lighting fixture U.S. Pat. No. 4,677,533 (McDermott) is typical of an invention that synthesizes a projected light beam from light sources of differing spectral distributions. This prior art creates the color balance by the adjustment of several potentiometers and does not use the electrical/electronic characteristics of the lamps to maintain the proper spectral distribution when a reduction of power occurs.
Incandescent lamps are traditionally used for this type of lighting device but they are not adequate as they experience dramatic changes in the color of the projected light as the power consumed by the lamp is decreased. They are also inadequate because they can provide only a limited spectral distribution. A related invention is disclosed in U.S. application Ser. No. 07/208,218, now pending.